#define _CRT_SECURE_NO_WARNINGS 1
struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode() : val(0), left(nullptr), right(nullptr) {}
    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
    TreeNode(int x, TreeNode* left, TreeNode* right) : val(x), left(left), right(right) {}
    
};

class Solution {
public:
    TreeNode* invertTree(TreeNode* root) {
        if (root == nullptr)
            return nullptr;
        TreeNode* left = invertTree(root->left);
        TreeNode* right = invertTree(root->right);
        root->left = right;
        root->right = left;
        return root;
    }
};